High compression vane pumps which are driven in opposite directions to pressure and deflate an associated system are characterized by having clearance between the moving and stationary parts of the pump. In order to reduce the need for expensive filtration units it is desirable to provide clearance between movable and stationary components so that they will be insensitive to contaminants in the stream of fluid being pumped. Moreover, another problem is how to reduce high starting torques in motor pump assemblies while retaining a desired high pressure output at high speed operation.
In known vane type pumps it has been necessary to provide close clearances between the moveable components of the pump and its stationary components. In such arrangements the reduced clearances for producing the high pressure discharge capabilities will create frictional drag between the moveable parts which in turn will produce a high starting torque that can only be produced by larger drive motors.
U.S. Pat. No. 4,253,809 discloses a two part rotor with end sealing surfaces. There is no provision in the pump for reducing friction only during start-up so as to reduce the need for larger drive motors.
U.S. Pat. No. 4,032,268 discloses a rotor supported by a plurality of axial thrust bearings to vary axial thrust and face clearance in accordance with engine temperature. It does not address the problem of how to reduce torque on engine start-up while maintaining engine compression when it is up to speed.
U.S. Pat. No. 3,528,757 discloses a rotor supported and positioned by a curved bearing and an adjustable screw for controlled axial clearance. Again there is no provision for reducing torque on start-up.
Japan 0066882 of Apr. 5,1986 entitled "Compressor with Ceramic Rotor" discloses a rotor having a steel shaft and a ceramic rotor part to control thermal expansion so as to maintain clearance between the rotor and the pump housing. The arrangement does not adjust clearance at start-up and at high speed operation.
While the aforesaid pump and rotor configurations are suitable for their intended purpose, e.g., thermal compensation to prevent excessive torque during high temperature operation, their is no provision therein to produce a change in the clearance between rotating and stationary components of a pump during start-up and at high speed operation of the pump.